It is known to employ copper-containing aqueous solutions as biocide fluids, for example, for the pressure treatment of lumber and for water purification. Copper-containing solutions may be produced by reacting copper oxide with chromic acid and arsenic acid to produce a solution of the copper with chrome and arsenic. The solution is subsequently diluted with water and the resulting aqueous solution may be injected into wood under pressure. This chromated copper arsenate (“CCA”) is the primary additive used in the treatment of wood against termite and other biological infestation. Although the CCA is very effective, it has come under increased pressure because of the environmental concerns associated with chromium and arsenic.
A new generation of pesticide is now emerging that appears to be efficacious, and which relies on the use of copper (in larger quantities than in the CCA) in combination with other pesticidal components, such as quaternary amines and triazoles. The copper is typically applied as a solution of the monoethanolamine complex of copper carbonate or borate. The commercial form of the copper concentrate usually contains about 100 to 130 g/l copper which is diluted with water prior to injection into the wood. It is known to dissolve copper in the presence of alkanolamines such as MEA in the presence of air and carbon dioxide. As described in co-owned U.S. Pat. No. 6,646,147, the copper complex is typically produced commercially by the dissolution of basic copper carbonate in a solution of monoethanolamine (MEA), followed by further carbonation or addition of boric acid. The reactions can be approximately represented by the following equations:CuCO3Cu(OH)2+7MEA→Cu(MEA)3.5CO3+Cu(MEA)3.5(OH)2 Cu(MEA)3.5(OH)2+CO2 (or Boric acid)→Cu(MEA)3.5CO3+H2O
The copper carbonate precursor is expensive, relative to scrap copper metal, and a brine waste is generated by the above process which gives rise to environmental concerns. It is known from the prior art that ammonia and carbon dioxide added to water can be used to dissolve copper metal with oxygen from air as the oxidant. This is represented by the following equation:Cu+2NH3+(NH4)2CO3+½O2→Cu(NH3)4CO3+H2OThe reaction proceeds well and has been the basis for copper dissolution in several commercial facilities.
Other examples of dissolution of copper or copper salts utilizing such fluids and uses thereof may be found, for example, in U.S. Pat. No. 4,929,454 and U.S. Pat. No. 6,294,071. The copper-containing solutions may be formulated, for example, by dissolving copper in aqueous solutions containing alkyl amines or alkyl hydroxy amines, such as 2-hydroxyethylamine. U.S. Pat. No. 6,294,071 states “in one conventional batch process for producing copper-containing amine solutions, approximately five days is required to achieve the target copper concentration (i.e., about 8%),” and subsequently discloses a method to dissolve copper that requires the imposition of a galvanic or electrolytic driving force to accelerate the process to provide a product after dissolution “of about one day”. The use of electricity is not desirable, as the energy costs can be significant, and the process (having large electric current flows through flammable and/or explosive solvents) is inherently hazardous.
U.S. Pat. No. 5,078,912 discloses a composition that contains copper, MEA, free alkali, and a salt of a fungicidal anion (such as fluoride, borate, or fluoroborate). The process of manufacture of this composition comprises dissolving copper salts, e.g., copper carbonate. U.S. Pat. No. 4,808,407 discloses a process to prepare water soluble copper salts of carboxylic acids, said acid containing from about 10 to 30 carbon atoms. The dissolution of copper powder with air in the presence of MEA is described. U.S. Pat. No. 4,324,578 discloses a process to prepare an algaecide using copper carbonate, MEA, and triethanolamine.
The prior art processes using copper metal had kinetics which were very poor such that the process was unattractive from a commercial standpoint. The kinetics of the processes are improved if the amine is initially carbonated, but dissolution of 100 grams of copper into a liter of an alkanolamine/water mixture typically took 3 to 6 days. Co-owned U.S. Pat. No. 6,646,147, the disclosure of which is incorporated herein by reference, describes a process which accelerated the dissolution rate of copper in a partially carbonated aqueous MEA solution to a rate where copper-MEA-carbonate compositions could be formulated at rates (and costs) that made this process commercially feasible for the wood preservative market. The kinetics of the processes are further improved if the partially carbonated aqueous MEA solution comprises a small amount of dissolved copper, and dissolution of 100 grams of copper into a liter of a partially carbonated aqueous MEA solution can be achieved in under 6 hours.
A need exists for additional efficient, fast, and inexpensive processes for producing copper containing aqueous solutions, suitable for use in the wood-treatment industry. The present invention seeks to fill that need.